1. Field of the Invention
This invention generally relates to semiconductor manufacturing equipment and, more particularly, to equipment for rapid thermal processing of a semiconductor wafer.
2. Description of Related Art
To make semiconductor devices of decreased dimensions, new processing and manufacturing techniques have had to be developed. One important requirement for the new techniques is to be able to reduce the amount of time that a semiconductor wafer is exposed to high temperatures during processing. One such processing technique designed to address this requirement is know as Rapid Thermal Processing (RTP). The rapid thermal processing technique, typically includes quickly raising the temperature of the wafer and holding it at that temperature for a time long enough to successfully perform a fabrication process, while avoiding such problems as unwanted dopant diffusion that would otherwise occur at the high processing temperatures.
Generally, conventional RTP systems use a light source and reflectors to heat the bulk of the semiconductor wafer. The light source is usually a bank of Halogen lamps that emit radiation energy that is focused on the wafer by the reflectors.
Conventional Halogen lamp-based RTP systems have considerable drawbacks with regard to achieving and maintaining a uniform temperature distribution across the active layer of the wafer surface. For example, the Halogen lamp has a filament, which generates broadband radiation. By applying more power to the filament, the intensity of the lamp can be increased. However, silicon wafers are heated using a useable band of short wavelengths, and are otherwise transparent to wavelengths outside of this band. The peak intensity of the lamp tends to increase the wavelengths outside of the useable wavelength band. As a consequence, much of the applied power is wasted.
Another drawback to filament type lamps is that they generally create a wavelength distribution that is non-uniform and independently uncontrollable. Consequently, temperature fluctuations occur on the surface of the wafer which may cause crystal defects and slip dislocations in the wafer at high temperatures (e.g. xcx9c1000xc2x0 C.).
One particular solution to the drawbacks of Halogen lamp-based systems is disclosed in U.S. Pat. No. 5,893,952. In the 952 patent, an apparatus is described for rapid thermal processing of a wafer using a narrow band beam of electromagnetic radiation generated by a high wattage laser. The beam is directed at the wafer, through a thin absorption film, which absorbs substantially all the energy from the beam, which, in turn, radiates heat to the wafer. Unfortunately, the apparatus described above has some limitations and drawbacks. For example, the thickness of the thin film must be accurately determined. If the thin film is too thin, energy from the beam may be transmitted directly to the wafer, or if the thin film is too thick the film may not heat up fast enough for rapid thermal processing. A film must be used that does not degrade over time, and must not sputter, bubble, or degas when heated, otherwise non-uniform absorption will result. Because of the requirements placed on the thin absorption film, the materials for this film are limited. As a result, the same RTP apparatus may heat wafers differently and unpredictably, which wastes both time and materials.
For the above reasons, what is needed is an apparatus, system, and method for uniformly and controllably heating the surface of a semiconductor wafer during rapid thermal processing.
The present invention provides an apparatus, system, and method for uniformly and controllably heating the active surface of a semiconductor wafer during processing. The present invention may include a scanner assembly which is operable to scan over a single semiconductor wafer. As described in greater detail below, a radiation energy source is provided enclosed within the main body of the scanner assembly. The radiation energy source may be surrounded by a reflective/absorptive surface, which both reflects and absorbs the radiation, emitted from the energy source such that the resultant energy output as seen by the wafer is substantially free of non-uniformities. The reflected energy is directed through a slit in the scanner assembly. Advantageously, the narrow band of energy allowed to escape the scanner assembly is uniformly scanned over the wafer to heat only the active layer of the wafer surface. Because the beam is uniform over the diameter of the wafer there is no heating overlap.
In one aspect of the present invention, an apparatus is provided for rapid thermal processing of a wafer. The apparatus includes a radiation energy source, preferably a filament-less lamp. The apparatus further includes a scanning assembly operable to scan a beam of the radiation energy across the surface of a wafer. The radiation energy is used to heat an active layer of the wafer.
In another aspect of the present invention, an apparatus for rapid thermal processing of a semiconductor wafer is provided. The apparatus includes a housing which defines a reflecting chamber. Within the reflecting chamber is disposed a radiation energy source. To allow at least a portion of the radiation energy to escape the reflecting chamber, a radiation outlet channel is also provided. Also provided is a scanner, which is operable to scan the radiation energy escaping from the reflecting chamber across the surface of a wafer to heat an active layer of the wafer.
In yet another aspect of the present invention, a method is provided for rapid thermal processing of a semiconductor wafer. The method includes providing a source of radiation energy and scanning a semiconductor wafer with a narrow band of the radiation energy to raise the temperature of an active layer of the semiconductor wafer.
Because the scanning RTP system of the present invention is designed to heat only the active region of the wafer surface, the process is advantageous for implant anneal applications, such as shallow junction, ultra shallow junction, and source drain anneal. The scanning RTP system may also be used effectively for thermal donor annihilation, recrystallization, and H2 anneal. Moreover, since the bulk of the semiconductor wafer need not be heated during the heating process, the amount of power used by the RTP system can be reduced to less than 50 kWh, preferably, less than about 10 kWh. Similarly, scanning times, and therefore processing times, may be reduced since only the active surface of the wafer is being heated.
These and other features and advantages of the present invention will be more readily apparent from the detailed description of the preferred embodiments set forth below taken in conjunction with the accompanying drawings.